1. Field of the Invention
The present invention relates to a light guide sheet and a movable contact element using the sheet, which are used to operate various electronic apparatuses.
2. Background Art
In recent years, an increasing number of electronic apparatuses such as portable telephones and other portable terminals have come to use light emitting diodes or EL (electroluminescent) devices as light sources to illuminate their operating parts. The illumination allows the user to easily distinguish between push buttons or to operate the display in dark environments. In line with this trend, movable contact elements and switches used in these apparatuses are also expected to be more user-friendly and capable of being variously illuminated.
FIGS. 6 and 7 are a sectional view and a plan view, respectively, of a conventional switch. In FIGS. 6 and 7, the dimensions of some parts are exaggerated for clarity.
The switch includes movable contact element 6 having light guide sheet 3, which is formed of light-transmissive, film-like base material 1 and irregular-shaped light extracting elements 2 arranged in predetermined positions on the top surface of base material 1. The switch also includes film-like cover sheet 4 whose outer periphery is pasted at predetermined positions on the bottom surface of light guide sheet 3 via an adhesive (not shown). The switch also includes dome-shaped movable contacts 5, which are formed of a conductive sheet metal and pasted on the bottom surface of cover sheet 4 under light extracting elements 2.
The switch also includes wiring board 7, which is provided on its upper and lower surfaces with wiring patterns (not shown). Wiring board 7 is also provided on its upper surface with fixed contacts 8 each consisting of circular central fixed contact 8A and horseshoe- or ring-shaped outer fixed contact 8B surrounding central fixed contact 8A. Movable contact element 6 is pasted on the top surface of wiring board 7. More specifically, the outer peripheries of movable contacts 5 are placed on outer fixed contacts 8B, and the centers of the bottom surfaces of movable contacts 5 are predeterminedly spaced from central fixed contacts 8A.
The switch also includes light-emitting devices 9 composed of light emitting diodes or the like arranged on sides of light guide sheet 3 on the top surface of wiring board 7. Light-emitting devices 9 are arranged with their light emitting surfaces facing one side of base material 1.
The switch also includes light-transmissive, film-like display sheet 10, which is provided on its bottom surface with light shielding part 10A formed by printing or the like, and display parts 10B hollowed out in the shape of characters, symbols, and the like. Display parts 10B are arranged over light extracting elements 2 of light guide sheet 3.
The switch thus structured is installed on the control surface of an electronic apparatus, with central fixed contacts 8A, outer fixed contacts 8B, and light-emitting devices 9 connected to electronic circuits (not shown) of the apparatus via the wiring patterns.
When the user presses one of display parts 10B of display sheet 10, light guide sheet 3 and cover sheet 4 are bent to press the dome-shaped center of movable contact 5 that corresponds to the pressed display part 10B. When a predetermined compressive force is applied, movable contact 5 is elastically inverted downward with a click feeling. As a result, movable contact 5 comes into contact at the center of its bottom surface with central fixed contact 8A, thereby electrically connecting central fixed contact 8A and outer fixed contact 8B.
When the user releases the compressive force applied to display sheet 10, movable contact 5 is elastically inverted upward by the elastic returning force. As a result, the center of the bottom surface of movable contact 5 is separated from central fixed contact 8A, thereby electrically disconnecting central fixed contact 8A and outer fixed contact 8B.
The electrical connection and disconnection of fixed contacts 8A and 8B switches the functions of the apparatus. When power is supplied from an electronic circuit of the apparatus, light-emitting devices 9 emit light, which is introduced into light guide sheet 3 from one side of base material 1 and propagates inward while being reflected in base material 1.
The light is diffused and reflected by light extracting elements 2 formed on the top surface of base material 1 so as to illuminate display parts 10B of display sheet 10 from below. Illuminating display parts 10B allows the user to easily distinguish between the characters, symbols, and the like on display parts 10B in dark environments.
In the conventional switch, as described above, when the user presses somewhere on display sheet 10 so as to press the top surface of light guide sheet 3, the corresponding movable contact 5 is elastically inverted, thereby electrically connecting or disconnecting fixed contacts 8A and 8B. The light of light-emitting devices 9 is introduced into light guide sheet 3 from one side of base material 1 so as to make light extracting elements 2 emit light, which illuminates display parts 10B of display sheet 10. A conventional technique related to the present invention is disclosed in Japanese Patent Unexamined Publication No. 2007-87749.
In the conventional switch including movable contact element 6 using light guide sheet 3, the light of light-emitting devices 9 is introduced into base material 1 from one side thereof to make light extracting elements 2 emit light concurrently, thereby illuminating display parts 10B by light of one color. Attempting to illuminate display parts 10B by light of different colors using light-emitting devices 9 having different luminous colors would require more than one light guide sheet. This would increase the number of components and assembly time.